We have found embryonic muscle and nerve cells in culture rapidly replenish and enzyme, acetylcholinesterase (AChE) after it has been inhitited by organophosphates like diisopropylfluorophosphate (DFP) and paraoxon. The AChE synthesized, moves through the cells and into the medium surrounding them. This year we propose to examine whether organophosphates that cause a delayed neurotoxicity in chickens and man will also have long-terminjurious effects on nerve cultures and whether a lose of regulation of AChE and muscle damage is an early response of animals poisoned with a single dose of these agents. We continue to work on the regulation of AChE in cultured muscle and nerve, examining whether stimulation and acetylcholine analogs will affect nerve AChE levels as we have shown they do for muscle. Finally, we are examining the number of subunits and the properties of the AChE forms present in the cells to find out whether they can be differentially inhibited by various treatments and localized under the electron microscope. Last year's studies showed that AChE in muscle could be regulated, in part by muscle activity. This year's studies shift part of the research from muscle to nerve, following, in cell culture, the path by which neural influences control muscle. Bibliographic references: Walker, C. R. and Wilson, B. W. 1975. Control of acetylcholinesterase Walker, by activity of cultured muscle cells. Nature 256, 213-216. Linkhart, T. A. and Wilson, B. W. 1974 Acetylcholinesterase in singly and multiply innervated muscles of normal and dystrophic chickens. II. Effects of Denervation. J. Exp. Zool. 193, 191-200.